Process for the recovery of toluene



April 2, 1946. c, R, CLARK 2,397,839

PROCESS FOR THE RECOVERY OF TOLUENE Filed Nov. 26, 1940 ATTORNEY Patented Apr. 2, 1946 UNITED STATES PATENT ori-lcs v l.3,397,839V alszslshlrslrnpringiield Township, Monttion' gomery County, Pa., assignor, by mesne assignments, to Allied Chemical & Dye Corpora- Application November 26, 1940, Serial No. 361,227

6 Claims.

This invention relates to a process i'or recovering toluene from mixtures containing it and other organic liquids.

Numerous hydrocarbon oiis are known which contain toluene in varying proportions. For example, catalytic treatment of a suitable petroleum fraction in the presence of hydrogen, gives an oil consisting chieily of hydrocarbons of both aromatic and non-aromatic character, and containing about 20% toluene. Gasoline fractions obtained by the distillation of certain types of petroleum frequently contain substantial Proportions of toluene, although mainly consisting of other, hydrocarbons. Oils of petroleum origin having a considerable content of aromatics, including toluene, may be treated bywell known selective-solvent processes to produce fractions rich in aromatics; for example, extraction of suitable fractions of such petroleum oils with sulfur dioxide may yield fractions of high toluene content. In such cases -toluene is accompanied by Ytlllation. Accordingly, recovery of'toluene of a relatively high purity from these sources presents a diilicuit problem of great industrial importance.

, For many purposes'to which toluene is put, it is desirable to use as pure a material as may be economically available. For example, toluene is largely used for the production of TNT, for which purpose a sol-called lnitration grade of toluene is now preferred. 'While toluene products. containing substantial proportions `of certain hydrocarbon oils other than toluene can be nitrated, the mono-nitro compound made from them must be purified prior to complete nitration. This materially increases the costand complexity of the non-aromatic oils which may be largely paraflinic, naphthenic or olenic in character. A considerable portion of these oils cannot be completely separated from the toluene by direct fractional distillation because of the closeness of their boiling points to that of toluene or because they form constant boiling mixtures with toluene.'

Furthermore, while ordinarily toluene is `readily separable by direct fractional distillation from light oils produced by the gasification of coal, in

some cases the toluene is accompanied `by rliiliv cultly separable non-aromatic oils of the same general character as described, owing to carbonization conditions, type of coal used or other special circumstances. Also synthetic hydrocarbon gas mixtures produced by`various catalytic processes may contain toluene which, when recovered, is accompanied by similar dimcultly separable constituents.

By fractional distillation of these oils containing toluene, fractions relatively high in toluene content may be obtained. These toluene fractions, however, will still contain large amounts of the other constituents of lthe oil having boiling points in the neighborhood of the boiling point of toluene or forming mixtures of constant boiling points in the range of temperatures at which' toluene distills from the oil. For example, by distillation of the above described types pears to represent a productor maximum toluene concentration obtainable .by direct fractional disof oils con. taining toluene under the most efllcient .condiprocess for making TNT. Furthermore, even though toluene containing substantial quantities of certain other materials is sometimes used for nitration, this is only becausethe dimculties 'of preparing a pure toluene have outweighed the disadvantages of using the impure toluene for the production of explosives. Direct fractional distillation, Ibecause of the 4diillculties pointed out above, will not effect a recovery of pure toluene from oils such as enumerated and in lmany cases will not give fractions of suitably highy toluene content or free from materials which even in small concentrations adversely' affect the nitration of the toluene or the nitrated produca The separation of the toluene from materials distilling from the toluene oil fraction at temperatures substantially higher or lower than the toluene does not present any great technical difilculties. 'I'he difficulty in recovering pure toluene from an oil fraction containing it, such as those referred to above, is presented by the problem of separating the toluene from the like-boiling, nonaromatic hydrocarbons; i. e., from those hydrocarbons which by direct fractional distillation processes as commonly operated for the fractional distillation of oils, distill from Vthe toluene fraction within the same temperature range as the toluene distills therefrom.

It is an object of my invention to provide 'a process whereby toluene of any desired degree of purity may be recovered from -oils containing it and other hydrocarbons which distill out over the same temperature rangeas the toluene.

I have now discovered a relatively pure toluene, e. g. toluene accompanied by no more than 5% of the hydrocarbon impurities of similar boiling range to that of the toluene, vcan be recovered from many oils containing toluene and other hydrocarbons by an azeotropic distillation of the oil under the conditions hereinafter described.

In using my invention for the treatment of an oil such as has'been described above, containing toluene and other hydrocarbons, particularly when the toluene concentration of the oil is low or the oil is one containing materials of wide boiling range, I prefer nx-st to fractionally distill the oil to recover therefrom van enriched toluene fraction whichv contains, in addition to toluene, other hydrocarbonswhich distill at the same temperatures `as the toluene. fractions having an end boiling point substantially vabove the boiling point of toluene (e. g; a

boiling point up to 118 C.) may be azeotropically Although toluene fractional distillation. In addition, the ratio of p-dioxane to hydrocarbons inl the distillates is unusually favorable. The ratio of p-dioxane to 'non-toluene hydrocarbons varies from about 55 to 45 at the start of a distillation of toluene fraction with p-dioxane to about 65,1; 35 when the non-toluene hydrocarbons have been practically distilled in themanner hereinafter described, I prefer the toluene fraction recovered in the preliminary distillation step be one having a maximum boiling point substantially corresponding to the boiling point of pure toluene; i. e., 111 C. Further, for the reasons which will be more speciilcally pointed out below, I prefer that the toluene fraction recovered by the preliminary exhausted from the material being distilled.

"These ratios are reasonably economical, entailing handling of not too great a volumeof azeo- -tropic distillates. The ratio of p-dioxane-to toluene vaporized in the distillation is far higher, i. e. close to 93 to 7. Such a mixture is highly eiective as a scrubbing medium for the toluene vapors. Yet such a mixture, which would be more uneconomical to distill, does not go over as distillate until the objective of the process of this invention is accomplished; i, e., until the non-toluene hydrocarbons have been distilled over and separated distillation of the crude toluene oil be so cut as to exclude therefrom the forerunnings which do not contain substantial proportions of toluene, for example, to exclude any materials -distilling below 100 C.

A toluene fraction such as may be obtained by this preliminary distillation, which may contain paraflins, naphthenes, or olens, is vsubjected to a second distillation in the presence of an azeotropic agent. An important factor in this azeotropic distillation of the toluene fractions is the provision of an azeotropic agent-which sharply separates the tolueneand the like-boiling, non-aromatic hydrocarbons so that a high yield of toluene of a desired purity may be obtained in distilling the to1uene fraction. It is highly desirable, from an economic standpoint, that the azeotropic agent,

from the toluene which remains in the residue at this point in the distillation. These characteristics of the p-dioxane contribute materially to its effectiveness as an azeotropic agent in the distillation of toluene oil fractions.

In its more specic aspects my invention com-` prises azeotropically distilling a toluene fraction containing like-boiling, non-aromatic hydrocar-V bons with rectication of the levolved vapors in in addition to its ability to separate the toluene and like-boiling hydrocarbons sharply, also should have'a high capacity for carrying over as distillate the non-aromatic hydrocarbons; i. e., an agent which forms' with these hydrocarbons azeotropes having a high 'ratio of hydrocarbons to azeotropic agent.v According, it is an object of this invention to provide a process for azeotropically distilling a toluene oil in the presence of an azeotropic agent which is: particularly eiective for separating the toluene from like-boiling, non-aromatic hydrocarbons contained in the toluene oil.

I have discovered that p-dioxane (para-dioxane) is particularly eiective when used for the azeotropic distillation of toluene fractions to separate the toluene from the like-boiling, non-aromatic hydrocarbons. Accordingly, my invention broadly comprises fractionally distilling a toluene oil containing like-boiling, non-aromatic hydrocarbons in the presence of p-dioxane.

` I have foundA that commercial dioxane nowy available, consisting almost entirely of p-dioxane, is a suitable azeotropic agent. While this material is sold with a wide boiling range specification, e. g. 95 to 103 C., actually its boiling range is usually much less, e. g'. within 4 C., the maj or portion distilling over within 1. C. It Aappears p-dioxane forms a low boiling azeotrope with toluene. I have discovered, however, p-dioxane forms with the non-aromatic hydrocarbons low boiling Aazeotropes which may be separated by fractional distillation from the toluene or any azeotropes which may be formed by the toluene and p-di oxane, There is a relatively wide spread between the boiling points of the azeotropes of the like-' boiling, non-aromatic hydrocarbons and of toluene or any azeotrope of toluene and dioxane which facilitates the separation of these materials by the presence of p-dioxane while maintaining at a point in the rectification of the vapors a temperature not above substantially 102 Cfunder i substantially anhydrous conditions and not above substantially 85 C. in the presence of water until the unvaporized residue contains at least 95 parts by weight toluene for. every 5 parts by weight ofvr said like-boiling hydrocarbons. These `temperatures are hereinafter referred to as a "control temperature. y Y v Regulation of the temperature in the rectication of the vapors to meet the conditions set forth above is accomplished by maintaining an adei quate quantity of the azeotropic agent present hydrocarbons of similar boiling range will be accomplished.

After the distillation has been carried to the point at which the residue containing toluene has thedesired purity with respect to hydrocarbons ofy similar boiling range to toluene, the distillation may be stopped and the residue withdrawn from the still. This residue ordinarily will con-'- tain toluene and other hydrocarbons in the proportion of 95 or more parts toluene to 5 or less parts of total hydrocarbons other than toluene;l It may be puried further, as desired, toremove any vazeotropic'agent it contains and to remove'.

any other impurities present. When the distillation has been carried to the point at which the hydrocarbon portion of the residue has a toluene content of 99% or more, the residue, after removal of residual azeotropic agent (if any), and

if necessary after a conventional reiining treat-- ment such as a sulfuric acid treatment followed by redistillation, is suitable for marketing as a i ynitration grade toluene of particularly high Purity.

Instead of withdrawing the toluene residue f toluene may be separated'from the distillate in any suitable manner, for example by extraction with a liquid which will form separate layers, one v containing the toluene and the othercontaining the dioxane. Water is a suitable liquid for eiecting this separation. In the absence of the dioxane, in distilling out the toluene the temperature in the rectification column may rise to the boiling point of toluene under the conditions prevailing as to pressure, etc.

The toluene fraction treated in accordance with my invention preferably will contain little, if any, hydrocarbons dlstilling from the hydrocarbon-toluene fraction at temperatures materially above those at which toluene distills therefrom. On the other hand, high boiling materials may be left with the toluene residue at the conclusion of the azeotropic distillation of the toluene fraction under the conditions set forth above to separate the toluene from the hydrocarbons .of similar boiling range. Once this separation has been effected, the toluene'inay be separated from the high boiling hydrocarbons by fractional distillation in the absence 'oi an azeotropic agent. Whether or not high boiling constituents should be left in the toluene fraction to be azeotropically distilled or whether, if left in the toluene fraction, they will remain in the residue after azeotropic distillation, depends upon a number of factors, among which their boiling range and chemical characteristics are important. If the constituents form azeotropes with the dioxane which have boiling points close to the above control temperatures of 102 C. and 85 C. for anhydrous conditions and in the presence 'of water, respectively, it is preferable to separate them by a direct fractional distillation before azeotropically distilling the toluene fraction. If they do not form azeotropes having boiling points close to the foregoing temperatures or if their amount is small, this procedure is not so important.

It is preferred thatthetoluene fraction subjected to azeotropic distillation in accordance with my invention be a fraction boiling in the range of 100 C. to 111 C. Such a fraction may be azeotropically distilled by my process and pure toluene obtained with a relatively small quantity of azeotropic agent lpresent during the distillation. Pure toluene may be obtained byy distilling with p-dioxane a toluene fraction boiling, for

condenser. I is divided in controlled proportions. One part of the condensate is returned ythrough pipe I to the top of columnl' and'reiluxed in con-` tact with the vapors rising in the column. The other portion ofthe condensate is withdrawn through pipe 8. Two receivers 9 and I0 are connected to pipe 8 through valve-controlled branch .pipes II andv I2 so that the condensate drawn ofi through pipe a may be divided and distributed' as described below to the two receivers.

` Receiver I0 is connected by a pipe I3 controlled by valve I4 with a second still I5. Still I5, like still I, is provided with a heater I6, a rectication column Il, a condenser I8 and pipes I9 and controlled by valves 2| and 22 for return of determined proportions of condensate from condenser I8 to the top of column I1 and withdrawal of another portion of the condensate through example, from 95 C. to 118 C. but the quantity of the dioxane present inthe distillation of the toluene fraction of wider boiling range must be substantially increased as compared with the quantity which suillces for distilling the fraction of the narrower boiling range.

My invention will be more particularly illustrated a"nd described in lowing examples.

The accompanying drawing diagrammatically' illustrates an apparatus suitable for carrying out the processes of these examples.

The apparatus of the drawing comprises a still I provided with a heater 2 and connected with a rectification column 3 and a condenser 4 for the vapors leaving the top of the column; By

conjunction with the ioll dpipe 20. Pipe 20 leads to a separator 23 into which water may be introduced from a pipe `24.

Example I In carrying out one embodiment of my invention in the apparatus described above, 'a liquid hydrocarbon mixture containing about 20% toluene by volume, the remainder substan-` tially consisting of other aromatic hydrocarbons and aliphatic and naphthenic hydrocarbons with only traces of oleflnes, was introduced into still I. This crude toluene material was .produced by catalytic treatment of a petroleum distillate in the presence of hydrogen. It had a specific gravity of 0.757 at 15.5 C. and distilled over a range of from 53 C. to 156 C.

The charge of this hydrocarbon mixture introduced into still I was boiled in the still and the evolved vapors were countercurrently contacted in column 3 with reflux from condenser 4, in which the vapors leaving the topvof the column were substantially entirely condensed. Most of the condensate from condenser 4' was returned through valve 5 and pipe 'l to the top of the column to furnish the reilux for the column, the remaining small portion of the condensate being continuously withdrawn through valve 6 and pipe pheric pressure; i. e., the pressurein condenser 4 and at the top of column 3 was substantially atmospheric. and the pressure in still I was only enough higher to force the vapor through the rectication column to the condenser.

When the vapor temperature in the top of colf umn 3 reaches 109.5 C., the condensate passing through pipe 8 is diverted to vessel I0. The cut -taken in vessel I0 includes the distillate coming over up to and at a temperature of 110.5 C.

at the top of the column. With emcient rectiflcation of the vapors in column 3 during the fractional distlllation of the crude toluene oil, the cut collected in vessel I0 contains about 76% by volume of toluene, as determined by the speciiic dispersion method for analyzing hydrocarbon oilsl described in Industrial i Engineering Chemistry, Analytical edition, vol. 11, page 614, November 15, 1939.

The toluene fraction collected in vessel I0 is subjected to .azeotropic distillation, which represents the second stage of this example.4 For this purpose the toluene fraction containing 76% toluene was introduced into still I5 together with p-dioxane in the proportions of 150 volumes of p-dioxane for every 100 volumes of the toluene fraction. The p-dioxane used was a commercial product having a boiling range of 97.5-1032? C.

and a freezing point of 10.1 C. Ninety per cent means of valves I and C, condensate flowing from of this material distilled between 100 and 102 tiveness of the fractionating column, and its mechanical construction, which determine the quantity of p-dio'xane required to provide vaporliquid equilibria throughout the column under actual operating conditions. The mixture of p-dioxane and toluene fraction was distilled with' rectication of the vapors in column l1 and condensation of the vapors leaving the top of the column in condenser i8. Most of the condensate was returned through pipe I9 to the top or column I1 while the remainder was withdrawn through pipe 20 to separator 23.

With adequate p-dioxane present to'eiect the desired separation, the major part of the non toluene hydrocarbons appears in the early dis--` tillate fractions accompanied by very little toluene; in this stagethe vapor temperature at the top of the column is below 100 C. The toluene content of the distillate then gradually increases and the vapor temperaturerises and flnally, when nearly pure toluene distills oyer with the p-dioxane, the vapor temperature stands at approximately 102 C. Azeotropes formed with the p-dioxane by the hydrocarbons other than toluene present in the toluene fraction introduced into still i have boiling points suiciently below that at which the toluene distills for ltheni to be preferentially vaporized and by rectiilcation in column H to be largely separated from -the toluene and any toluene-p-dioxane azeotrope which is vaporized in still IS and enters column II so long as` there issufllcient p-dioxane present in.the vapor` and liquid phases in the rectiiication column. As pointed out above, the requisite quantity of p-dioxane to be supplied is that which will maintain the temperature at a point in the rectication column, preferably at the top of the column, not above substantially 102 C. under the substantially anhydrous conditions of this examto 100%. At this point the distillation was discontinued. The residue left in still l5 may be Washed with water to remove p-clioxane. The oil layer which separates from a water-p-dioxane layer contains 100% toluene. The quantity of 100% toluene isolated in this manner represented 92% of the toluene originally present in the still charge.

w Almost all of the remaining 8% may be recovered in subsequent operations by collecting` separately the last distillate fractions. relatively rich in toluene, and re-using this material directly in a subsequent azeotropic fractionation of a toluene fraction, the p-dioxane serving as a source of azeotropic component in the fractionation. By agitating the distillate collected in separator 23` with water and allowing the liquid to remain quiescent fora short time, it will separate into two layers. The lupper layer is an oil containing the non-toluene constituents of the toluene fraction originally supplied to still I5 and the portion of the toluene carried over in the distillation. This oil may be treated or used as desired. The aqueous p-dioxane layer separated in treating the distillate with Water may be treated in any of the well known manners to recover p-dioxane therefrom for use in dis'tilling a subsequent batch of toluene fraction.

Example II.-The procedure of Example I may be modiiied to use p-dioxane in the azeotropic distillation of a toluene fraction obtained by distillingv in still I and columny 3 an oil containing about 20% toluene, 20% of other aromatic hydrocarbons and the remainder substantially consisto of aliphatic and naphthenic hydrocarbons and traces of oleiines. This crude toluene material lwas produced b y catalytic treatment ofv a petroleum distillate in the presence of hydrogen. It had a speciiic gravity of 0.760 at 15.5 C. and distilled over a range `of from 56 C. to 161 C. In distllling this crude toluene material a cut boiling over the range of l09.5 C. to 110.8 C. was taken 1 off in vessel l0 of the apparatus of the drawing.

This cut or toluene fraction may contain '16% 'by volume of toluene. A mixture of 20D-volumes of p-dioxane for every 100 Volumes of this toluene ple. p-Dioxane'is vaporized from the still, en-

ters the rectication column as vapor and in part is returned to'thecolumn as liquid in the condensate from condenser i8. If insufllcient p-dioxane is initially introduced in the charge to the still, additional p-dioxane, suillcient to maintain the requisite temperature in the rectincation column, may be supplied as the distillation progresses. This p-dioxane may be introduced either into the still or into the rectiiication column itself. The toluene is in large part returned down the rectication column and retained in the still,

while ythe azeotropes of the p-dioxane with the other hydrocarbons are distilled'out and are co1- lected in separator 23. The loss of toluene from the still to the condensate drawn on through pipe 20 will depend upon the eiliciency with which A the vapors are rectified. Efilcient rectification is employed in order to keep downv this loss of toluene.

In carrying out the process of this example, as the distillation continued the temperatureof the vapors 'at the top of column I1 rose from about 96 C. to 101.6 C. The' toluene content of the oil obtained from vthe condensate withdrawn' through pipe 20 by washing the condensate with `water to free it of p-dioxane increased from 3% about 98% toluene.

Y carbon oil containing about 98% toluene isobtained. The distillate may be extracted with Water to separately recover the oil and p-dioxane it contains. V

Numerous changes and modincations may be made in the above described processes without departing from my invention. While in the first dlstillationstep of the crude toluene oil it is preferred totake off a toluene fraction having 'an end Vboiling point of substantially 111 fC. and-fractions with ahigher end boiling point, such as 118 C., may be successfully distilled azeotropically toobtain pure toluene, even a larger leeway is permitted in the temperature at which the toluene fraction starts to be taken oii'; i. e., in the initial boiling point of the toluene fraction. Y Nevertheless, it is preferred the toluene fraction subjected to azeotropic distillation be one boiling 'in the As the distillation proceeds the temperarange of 100 c. to 111 c. such a fraction may be distilled in the azeotropic distillation step of my process and pure toluene obtained with a relatively small quantity of azeotropic vagent present I present in the distillation of the toluene fraction of wider boiling range must be substantially increased as compared with the quantit'y which sumces for distilling the fraction of the boiling range.

While I have described my process in conjunc-4 tion with examples in which the two distillation steps are batch procedures, either or both of theseV distillations advantageously may be carried out continuously by well known continuous distillaftion procedures suitable` for the fractional distillation of mixtures of two or more liquids.

The minimum ratio oi azeotropicagent to the toluene fractionn which is suitable for carrying narrower tion by the process of this invention reduces the effectiveness with which the toluene is separatedirl from the like-boiling, non-aromatic hydrocarbons and reduces the yield of toluene recovered.

The complex azeotropes containing water have lower boiling points than the simple azeotropes not containing Water. Thus, in distilling a mixture containing 100 volumes of the 76% toluene fraction and'30 volumes of the p-dioxane of Example I, and also containing i0 volumesof water,

the non-toluene hydrocarbons started distilling ou* my invention will vary with the amount and Y the particular batch or continuous procedure used,

the quantity of p-dioxane used in the distillation of hydrocarbons from a .given quantity of toluene fraction should be in excess of that which will form azeotropic mixtures with the non-toluene hydrocarbons which are to be vaporizedand taken V over into the distillate. This quantity of azeotropic agent includes 'fresh agent introduced into the material being distilled and also any of the azeotropic agent which may be separated from the y distillate and returned continuously or periodically to the still or rectification column while the distillation of the toluene fraction is progressing. Temperature readings are taken of the vapor at the top of the rectiilcation column and, by supplying additional p-dioxane when required to prevent this temperature from rising above the above described control temperatures, an adequate amount of p-Vdioxane will be present during the separation of the non-toluene hydrocarbons from the toluene fraction. It is not necessary that this point of control temperature be at the top of the column, although this is a satisfactory point for determining this temperature in the equipment used for fractionating the lvapors and condensing the fractionated vapors in the above examples for effective use of the rectification column. One skilled in the distillation art will recognize suitable points for maintaining this control temperature in any other specific apparatus according to well known distillation principles.

Water appears to form complex azeotropes with p-dioxane and toluene and like-boiling, non-aromatic hydrocarbons. -The spread between the boiling points of the complex azeotropes of water-dioxane-toluene and water-dioxane like-boiling, non-aromatic hydrocarbons is smaller than the spread between the simple azeotropes of the dioxane with like-boiling, non-aromatic hydrocarbons and toluene or its azeotrope with p-dioxane. Accordingly, the presence of water in azeotropically distilling a toluene fracover below 83 C. and when the temperature had risen to 84.5 C., the hydrocarbons in the distillate were 99% toluene. Although pure toluene may be recovered with suilicient water present in the distillation to form complex azeotropes with the hydrocarbons taken oil as distillate, in order to obtain high yields of toluene without having to fractionate the vapors being distilledto an unduly high degree, water is preferably excluded from .the materials in the azeotropic distillation of the toluene fraction with p-dioxane.

It is, of course, obvious that preliminary distillation of a crude toluene oil to obtain a toluene fraction suitable for recovery of toluenetherefrom by the azeotropic distillation need not be cerried out in immediate conjunction With` the azeotropic distillation. The toluene fraction may be produced in one plant, transported to and submitted to azeotropic distillation in another plant. Nor is my invention limited to any particular procedure for the production of the toluene fraction. My invention contemplates distilling with p-dioxane any oil containing toluene together with other hydrocarbons which, when the oil is distilled, vaporize therefrom in the same tempera- -ture range as the toluene and, therefore, are not whether produced by fractional distillation of toluene-containing materials or by any other means. y

In this speciflcation'I have described the azeotropic distillation of toluene fractions as carried out under substantially atmospheric pressure. It is, of course, possible to azeotropically distill the toluene fraction under pressures above or below atmospheric. In that case the vparticular temperatures used' as a control for the amount of azeotropic agent present in the distillation will correspond to the change in the boiling points of the p-dioxane and hydrocarbon mixtures with change in pressure. The temperatures as given in this specification and in the appended claims are corrected temperatures for one atmosphere pressure (760 mm. of Hg).

This application is a continuation-in-part of my copending application Serial No. 343,499, :filed July 1, 1940, and the process disclosed herein of fractionally distilling an oil mixture containing toluene, collecting a fraction of said oil containing not more than 83-85% toluene and, speciilcally, collecting a toluene fraction distilling over a range of distillation temperatures of more than l0 centigrade degrees extending from below to at least as high as the boiling point of toluene, and azeotropically distilling the toluene fraction in the presence of a material forming a low boiling azeotrope with toluene, is claimed in said copending application Serial No. 343,499.

In my copending application Seriall No. 347,993 I disclose and specically claim processes for dispara-dioxane and of water.

I claim: 1. The process for the recovery o! toluene from atoluene fraction containing the same and contilling a toluene fraction in th'e presence both ciA egeeasse vdistiller-,e with p-dioxane hydrocarbons present taining like-boiling, non-aromatic hydrocarbons which comprises distllling said toluene fraction and rectifying the distilledvapors in the presence in toluene.

2. The process for the recovery of toluene from a toluene fraction containing the seme andc'ontaining like-boiling, non-aromatic hydrocarbons which comprises distilling said toluene fraction and rectliying the distilled vapors in the presence of substantially water-free p-dioxane in an amount which selectively'carries over as distillate with p-diox'ane said like-boiling, non-aromatic hydrocarbons and leaves a hydrocarbon residue oi the distillation enriched in toluene.

3. The process for the recovery of toluene which comprises distilling an oil fraction con taining toluene and like-boiling non-aromatic hydrocarbons which boils within the range.

fraction to separate the toluene from other hydrocarbons contained therein which dlstili from the toluene fraction in the same temperaturel range `as the toluene. distills therefrom, which comprises distilling said toluene fraction and rectifying the vapors evolved therefrom in the presence of pfdioxane in amount such that at a v point in the rectication of the vapors a temperature not above substantially 102 C. ls maintained until the unvaporized residue of the distillation contains at least 95 parts by weight of toluene' to every 5 parts by weight of other hydrocarbons which distill from a mixture consisting of the toluene and hydrocarbons in the same tempera-a ture range as the toluene, and thereby vaporlz ing and removing from said toluene fraction. as

therein which distill' therefrom, in the absence of said p-dloxane, inthe same temperature range as toluene contained therein.

5. The process for the treatment of a toluene fraction having an end boiling point not above 118 C. and containing parafilnic hydrocarbons,

- and which may also contain naphthenicand olenic hydrocarbons,'the aforesaid hydrocarbons distilling from the .toluene .fraction in the same temperature range as the toluene boils therefrom, which comprises distilling said toluene fraction and rectifylng the vapors evolved therefrom in the presence oi p-dioxane in amount such that at a point inthe rectification of the vapors a temperature not above substantially r102 C. is maintained until the unvaporized residue 'of the distillation contains at least 95parts by Weight o2 toluene to every 5 parts by weight of other hydrocarbons, and thereby veporizing and removing from said toluene fraction .as distillate with p-dloxane hydrocarbons present which -distill thereirom, in the absence of saldpdioxane, in the seme temperature range as toluene cohtained therein. y

6. The process for the recovery of toluene from a crude toluene oil produced by catalysis of a petroleum fraction in the presence ci hydrogen which comprises recovering from said crude oil a toluene fraction having an end boiling point of 111 C. containing paramnlc and naphthenic hydrocarbons, and which-may also contain olenic hydrocarbons, whichL hydrocarbons distill from said toluene fraction` in the same temperature range as the toluene distills therefrom, distilling said toluene fraction and rectifylng the vapors evolved therefrom' in the presence' of p-dioxane in amount such that a point in the rectication of the yapors a temperature not above substan- 40 tlally 102 C. is maintained until the unvaporized residue-oi the distillation contains toluene substantially completely separated iromthe parafnic and naphthenc and from any oleflnic hyf drocarbonswhich were present in seid toluene fraction, said last mentioned hydrocarbonsbeing carried over as ia distillate with p-dioxane and thus separated "from said residue containing toluene. 

